1. Field of the Invention
The present invention relates to an apparatus for controlling an industrial robot system and a method thereof, more particularly, to an apparatus for controlling an industrial robot system to perform a coordinated operation using a teaching playback method, and a method thereof.
2. Description of the Related Art
Conventionally, in a playback operation for performing a coordinated operation to a perform a task for simultaneously operating a tool moving apparatus for moving a tool and a workpiece handling apparatus for holding and moving a workpiece, it is difficult to maintain a pretaught constant relative speed of an end of a tool to a workpiece. This reason will be described with reference to conventional three methods, for example, in the case of moving a tool 2 of a welding torch from a point P1 to another point P2 on an elliptic trajectory using a straight line approximation method gradually changing an attitude of a workpiece 1, as shown in FIGS. 28a and 28b.
In the first conventional method, data of a large number of teaching points, into which the tool 2 is sequentially moved respectively as shown in FIGS. 29a to 29e, are stored as a task program in a storage unit, and then, these data are played back. In the playback operation, a starting timing and an end timing of the tool 2 of the welding torch are synchronous with those of workpiece 1. However, the tool moving apparatus and the workpiece handling apparatus have control units different from each other, respectively. Since these control units separately perform a calculation process for controlling operations thereof in this case, the relative speed between the tool 2 and the workpiece 1 during the operation always changes. Therefore, for example, when this method is applied to a welding process, the tool moving apparatus and the workpiece handling apparatus can not perform a coordinated operation with accuracy, and the welding process can not be performed so as to moving the welding torch along a desirable predetermined seem, resulting in considerably lowering quality of the welding.
As the second conventional method, a control method is suggested in the Japanese patent laid-open publication No. 63-216105, wherein control values of the tool moving apparatus and the workpiece handling apparatus are calculated, a relative position between a tool and a workpiece is calculated by detecting respective positions thereof during an operation, and then, respective control values are corrected according to the calculated relative position so that the tool and the workpiece are located in a desirable relative position. However, the tool moving apparatus and the workpiece handling apparatus have control units different from each other in a manner similar to that of the first conventional method, and these control units separately perform a calculation process for controlling operations thereof. Therefore, the relative speed between the tool and the workpiece during the operation always changes.
Further, as the third conventional method, there is suggested a method of correcting a detection value of a sensor after detecting a relative position of a tool to a workpiece using the sensor. In a conventional apparatus using this method, in order to perform a coordinated operation with high accuracy so as to move the tool and the workpiece in a predetermined constant relative speed, it is necessary to perform a high speed communication for exchanging information between control units of the workpiece apparatus and the tool moving apparatus. However, in the conventional industrial robot system, it is extremely difficult to obtain a high speed response in practice.